This invention relates to driveshafts, and more specifically to hollow aluminum alloy driveshafts.
In order to reduce the weight of a vehicle, lighter weight materials are being substituted for materials conventionally used in many applications. One application where a significant weight savings can be made is the substitution of an aluminum alloy for steel in the driveshaft or driveshafts of a vehicle. In a specific example of which I am aware, it was possible to reduce the weight of the driveshafts in a vehicle by 13 pounds (11.81 kilograms) for a 40% saving in weight by substituting aluminum alloy for steel in the driveshafts.
In my improved thin wall construction it is possible to reduce the weight of the driveshafts in the above example by another 11/2 pounds (1.36 kilograms) for an additional 7.7% saving in weight. I have found that the wall thickness necessary to transmit a given torque through an aluminum alloy tube can be reduced if the tube is hardened, and thus strengthened, by heat-treating. However, since the yoke portions of universal joints are joined to each end of the tube by welding, the tube loses substantially all of its hardness and strength due to the heat-treating in the area of the welds. Further, the areas of the tube adjacent the welds cannot be re-hardened by heat-treating without causing undesirable distortion of the yokes which are machined from heat-treated aluminum alloy. Therefore, I have provided a hardened aluminum alloy tube with the minimum wall thickness necessary to carry a given torque throughout most of its length. In the areas adjacent the welds where the tube has its hardness reduced due to losing the effect of the heat-treating in the process of welding the wall thickness is increased enough to transmit the given torque through an aluminum alloy tube without any increased hardness or strength due to heat-treating.